Generally, an amorphous silicon solar cell may be produced by a relatively simple process in comparison with a single crystal solar cell and it has been recognized that energy savings can be achieved by manufacturing at a low level of temperature, and with a thin film.
In promoting productivity, however, in an amorphous silicon solar cell it is always required that layers of the solar cell should be produced at a relatively high speed. Recently, considerable effort has been made to develop a process for rapidly growing layers of the solar cell by using a gas of silane such as Si.sub.2 H.sub.6 in order to promote productivity of the solar cell.
However, in the case where a solar cell is produced by a gas of monosilane which is relatively low in cost in comparison with a gas of Si.sub.2 H.sub.6 as mentioned above, it is required that the layers of the solar cell should be grown by means of controlling the level of the applied RF power generated due to the layers being grown slowly in the process therefor.
The RF power is utilized for a plasma discharging deposition in the process of growing the layers. Nevertheless, where a prior art amorphous silicon solar cell is provided with an intrinsic body, which is formed of relatively thick layers by using monosilane and the RF power is increased, as explained above, it has been found that efficiency of a solar cell converting sunlight into electricity has been reduced rapidly in connection with the RF power as illustrated in FIG. 2, and a problem has also been found in that the conversion efficiency as stated above has been reduced rapidly as shown in FIG. 3, even though the layers of the solar cell are grown quickly.